Chemical process



fuel.

Patented Mar. 23, 1943 CHEMICAL PROCESS Alfred W. Francis, Woodbury, N. J., assignor to Socony-Vacuum Oil Company, Incorporated, New York, N. Y., a corporation of New York No Drawing. Application June 28, 1939, Serial No. 281,651

3 Claims.

This invention relates to the production of high grade motor fuels. More particularly the invention relates to an improved method of synthesizing high grade motor fuels from olefines and paraifins of relatively low molecular weight.

In recent years the demand from the automotive and aviation industries for motor fuels of increased power has stimulated and commanded the attention of a tremendous amount of research. Since the compound iso-octane typifies high grade fuels, a large part of the research has been directed towards producing fuels consisting predominantly of compounds which approximate iso-octane; some other work has aimed at increasing the aromatic content of fuels. The processes developed for producing fuels of greater power are in general of three types, namely,

l e-arrangement processes such as cyclization and isomerism; pyrolysis or the selective breaking down of larger molecules to the molecules desired, e. g., de-polymerization and de-alkylation; and synthesis or the selective buiding up of smaller molecules to the molecules desired, such as alkylation and polymerization with hydroenation. 5 g

One of the more promising of the alkylation processes which has been developed is thesocalled cold-acid" process wherein isoparaflins are alkylated with free olefines (except ethylene) in the presence of a concentrated sulfuric acid catalyst at temperatures below about 30-40 C. The usual temperatures of operation in the "cold acid" process for alkylating with free olefines are from about 12 C. to about 30 C., and in order to eliminate as much polymerization of the olefines as possible, the concentration of olefines is kept relatively low by adding the olefines slowly to the reaction mixture. The sulfuric acid used in the "cold acid" process must be concentrated and its exact strength depends somewhat upon the particular olefines being used. For instance with propylene at about 20 C., the acid used is upwards of 100% and with isobutylene an acid around 9697% may be used. In this process only iso'paramns are alkylated, any normal parafilns that might be present are unaffected. Yields of high grade fuel appreciable above 100% based on the oleflne content are obtained.

It is an object of this invention to provide an improved method of combining paraflins and olefines to obtain high yields of high octane motor A more specific object of my invention is to provide an improved method of combining isoparaflins and olefines to obtain high yields of high octane motor fuel.

Still another specific object of my invention is to provide an improved method of combining isoparaflins and propylene at relatively low temperatures in the presence of sulfuric acid to produce high yields of high octance motor fuel which permits the use of less concentrated sulfuric acid.

My invention comprises an improved method whereby olefines are first reacted with sulfuric acid to form alkyl esters thereof and then the alkyl esters are reacted with paraffins in the presence of concentrated sulfuric acid at a relatively low temperature suitably adjusted with respect to the acid concentration that a high yield of high octane motor fuel is obtained.

It should be noted that all the reagents, i. e., all the alkyl esters and paraflins, should not be mixed in batch as poor yields will be obtained, but rather the reagents should be mixed slowly. In usual practice it has been found advisable to add the alkyl esters slowly to the parafiins over a period of, for example, about 'minutes. This time may vary with different operations and with .variations in yields that may be permitted; how- :ever, in any event, the mixing should be gradual and somewhat of this order rather than in batch.

Thus the alkyl sulfates in my process are added slowly to the reaction mixture as are the olefines in the cold-acid" alkylation with free olefines. However, the process of reacting an alkyl sulfate with an isoparaflln rather than using free olefiines as in the so-called cold-acid" process has several distinct advantages. In the first place, polymerization of oleflnes'is almost completely eliminated so that, for instance, in the case of diisopropyl sulfate and isobutane, at least of the product mayrconsist of branched chainheptanes. Further, gases which are relatively low in oleflne content may be employed in 'making the alkyl sulfates, since paraflinic gas diluents are unabsorbed. On the contrary when alkylating with free olefines mixed with a considerable concentration of other inert gases such as straight chain paraflins, e. g., propane or normal butane, the reactants are diluted, the pressure in the reaction vessel is increased and, production capacity of the apparatus is decreased. Since normal parafiins are commonly in admix ture with olefines supplies and since normal parafiins are inert in the so-called "cold acid" process such factor is a disadvantage. A further advantage in the use of alkyl sulfates rather than free olefines is that the absence of free olefines, 4

when using alkyl sulfates, diminishes the reduction and fouling of the acid catalyst so that it can be re-used more times, thus decreasing the consumption of acid.

. Perhaps the most important of the advantages of the. present process is the fact less concentrated acid can be used for the catalyst. As

indicated hereinabove the concentration varies,

is fouled more and hence can be re-used fewer times, or, at least, requires more expensive regeneration and replenishing.

I have discovered further that very important relationships exist between the temperature and acid concentration that may be used in my process if high yields are to be obtained. In order for a process to be commercially practical it should give a yield of at least 100% based on the olefine content, and preferably more. I have found that there is a lower limit temperature of operation below which such yields cannot be obtained. For instance, in working with propylene (i. e., using diisopropyl sulfate), at temperatures below about 5 or,7 C., it would be impossible to obtain high yields, since acid which is suflicientlyconcentrated for these temperatures of operation freeez's at such temperatures. For the above reason a temperature below approximately '7 C. cannot be used economically when reacting with diisopropyl sulfate unless possibly the freezing point of the acid is loweredin some manner which is not otherwise detrimental. On the other hand two high temperatures should not be used, as undesirable side reactions will be encountered. Temperatures around about 50 to 60 C. are at present considered optimum, and while we prefer to use temperatures around 50 to 60 C. or lower, temperatures up to about 100 C. could probably be used satisfactorily.

Furthermore, I have found that for the temperatures which are within the operative range, and can be used, there is a minimum acid concentration that can be used with each temperature, and below which high yields cannot be obtained. This discovery is fully illustrated in the following data obtained from reacting diisopropyl sulfate with isobutane under various conditions:

Table Concentra- Yield Tcmper- Conccntration Run No. (based on store tion plus $6 olefine) mm (Degrees C.) Per cent 98 52 08 2 95 9. 95% 2 97 21. 4 97 5 7 98. 5 117 99% 2t 93 04. 3 96% 2s 95 162 98% 26 97 178. 5 100% an 94. 5 m2 98 42 94. 5 13% 100% so 93 1M 100% so 94. 5 190 101% 50 95 188 102% so or, 180 103% 60 92 170 100% so 90 13s 9896 70 90 121 100 Runs 1 and 4 above were made at approximately the freezing points of the acids used, and,

therefore, were approximately the minimum temperature for that concentration of acid. Run 1 gave a poor result while run 4 gave a passable result just above the more or less arbitrarily considered commercially practical yield of 100%. Accordingly the 7 C. of run 4 might be considered to be approximately the lower temperature limit for obtaining high yields with diisopropyl sulfate.

It was further noted that an increase of about 7 C. permitted a reduction in the acid concentration of roughly 1%. Therefore a rule was formulated which appears to be suitable for roughly below 98 poor yields. were obtained. 0n theother hand, in all cases where this value was above 98, high yields were obtained. This rule probably applies more exactly near the middle of the operative temperature range than near the bottom or the top of this temperature range, and

while it is probably not a precise rule, it does serve to at least approximate operating conditions.

A further important feature of the present invention is the fact there are optimum temperatures around 50 to. 60 C. rather than aroundv 20 C. as in the cold-acid process. This advantake is realized because (1) temperature control by cooling water is cheaper than by refrigeration and (2) higher temperatures permit the use of weaker acid which is less fouled and can doubtless be used over again more times.

The above values will vary somewhat for olefines other than propylene and, in general, will permit wider limits because of the less reactivity of propylene. Because the conditions vary somewhat with the olefines used, to some extent with the parafllns used and various other factors, deiL nite limitations to all operating conditions ror all reactants could not be set feasibly. However such is believed unnecessary as I have indicated the general operating range setting forth many operable conditions and the precise limits of operation would in most cases be of little importance. Moreover, if desired, determination of the precise limits of temperature and acid concentrations that will give my improved results for any particular operation maybe easily made by a few tests as above outlined for diisopropyl sulfate and isobutane. The acid concentration in any operation of my process would not be below about 85% and for good results probably should never be below, about 90%. I

As mentioned, one of the advantages of the present process results from the fact that gaseous mixtures which are relatively dilute with respect K to oleflnes may be used as one of the raw materials. However, it is to be understood that any suitable source of oleiines may be used including pure olefines. The olefines which are used should be of relatively low molecular weight such as propylene and butylene so that when they are compounded with the paramn; the compounded molecules will have a boiling point within the gasoline boiling range.

The paraflins employed preferably comprise predominantly isoparaflins, for example, 150- butane and isopentane. These isoparaflins may be used in a pure form or may be mixed with other inert constitutents. Moreover, the isoparaffins may be used in admixture with normal the autoclave during 65 minutes.

sure to 42 lbs. and then dropped to 28 lbs.

Percent Initial Temperature, degrees centigradc.

an advantage over alkylation with free olefines wherein normal paraliins are inert constituents. Of course, if desired, only normal parafiins could be reacted with the alkyl sulfates. However. the yield in such cases is much lower and the resulting compounds have lower octane ratings.

In preparing the alkyl sulfates, the olefines or mixtures containing olefines, are reacted with concentrated sulfuric acid until substantially all,

The formation of diisopropyl sulfate, for in-- stance, may be carried out in the following manner:

Ninety-eight percent sulfuric acid is saturated with propylene using vigorous agitation and keeping the temperature below 0 C. One mole of acid absorbs 1.75 moles of propylene. The colorless product contains 0.75 mole of diisopropyl sulfate and 0.25 mole of isopropyl sulfuric acid.

If it is desired to neutralize the product, thisv may be done by washing with water and dilute alkali, leaving substantially pure diisopropyl sulfate, which is neutral, stable, and non-corrosive.

' Its specific gravity is about 1.1.

The following examples are given in order to further illustrate the invention. However, it is to be understood the invention is not to be limited thereto as there may be variations from these examples without departing from the scope of the invention:

Example I An injecting pump of 220 ml. capacity was filled with neutralized diisopropyl sulfate liquid prepared as outlined above. A Monel autoclave of 1060 ml. capacity was'charged with 430 ml. (796 g.) of 97% sulfuric acid and 300 ml. (1'77 g.) of liquid isobutane, and warmed to 20 C. at which the pressure was 35 lbs. Vigorous agitation was started, and .the ester was injected into The temperature rose gradually to about C. and the pres- Agitation was continued 30 minutes after all the ester was added, however such additional agitation is unnecessary.

The pressure was relieved, recovering 21 g. of excess isobutane. The product was poured out and separated into two. layers. The lower acid layer, 910 g., consisted of 95% sulfuric acid and small amounts of organic matter. The colorless upper layer of 0.680 sp. gr. was washed with 95%- sulfuric acid to remove traces of ester, then with 20% NaOH, and distilled, giving 288 ml., or 199 g., a yield of of the theoretical from the ester used 0 based on the olefinecontent. The portion boiling below 150 C. (84%, sp, gr. 0.680)

amounts to a 150% yield of this portion based on olefine content. The distillation range is as follows:

Fifteen other runs were made with diisopropyl sulfate and isobutane in a similar manner to that outlined above in Example 1, except that only 500 g. of acid were employed in each case. These runs are set forth in the table on page 2 hereinabove, and were made under various conditions of temperature and pressure as set forth in the table and gave the yields set forth therein. It will be noted that the greatest yield was obtained in run 11 using a temperature of 50 C. Theproduct of this run is also representative of the'product that may be obtained in general by my process. Thus, for instance, of the product of run 11 boiled between 165 and 200 F. which represents a yield of this fraction of 152% based on olefine content. This product had an octane rating of 87.2 neat and 97.9 with 1' cc. of tetra ethyl lead (1 be. per gallon).

Example II A reaction was carried out similar to that of,

Example I, but using isopentane as the paraflln, in place of isobutane, to. be reacted with diisopropyl sulfate. 500 g. of 98% sulfuric acid was used as the catalyst and the reaction temperature was room temperature, that is, about 26 C.

A yield of 84% based on the theoretical was obtained, or 228.5% based on the olefine content.

Example III A similar run to that of Example II, using iso- In order to show that the present process will effect the alkylation of even normal paraflins in the presence of sulfuric acid catalyst at low temperature, which has heretofore been considered impossible, a run similar to that of Example I was carried out, using normal butane in place of isobutane. While the yield was much lower, being only 10% based on the ester or 23.8% based on the olefine content, of which only about V3 was in the gasoline range, nevertheless it does show that an appreciable amount of alkylation does occur where heretofore it has been impossible to obtain any alkylation. Since most sources of isoparaflins do contain a certain amount of normal paraflins, it obviously is an advantage to have a process which will alkylate some of the normal paramns.

Thus it will be noticed that in all of the examples using proper conditions of temperature and acid concentration as set forth herein (except in the alkylation of normal paraflins), the yield of high grade motor fuel is well above based on the olefine content. Accordingly my invention affords a commercially feasible process of reacting alkyl sulfates with isoparafflns and thereby permits the enjoyment of all the advan tages of such process. 4

The yield in this case was 80% I claim:

1. The process of alkylating a paraffin with olefin which comprises absorbing the olefin in concentrated sulfuric'acid to form an absorption mixture thereof and reacting a parafin with the absorption mixture of olefin and concentrated sulfuric acid in the presence of concentrated sulfuric acid under alkylation conditions of operation to efiect alkylation of the paraffin with said olefin, said alkylation reaction being carried out at a temperature between about 50 and about 60? C. and in the presence of sulfuric acid of such concentration that the percent concentration of the acid used plus one-seventh of the temperature used in'degrees centigrade equals a numerical value of at least 100.

- 2. The process of alkylating an isoparaflin with propylene which comprises absorbing the propylene in concentrated sulfuric acid to 'form anabsorption mixture thereof and reacting "an isoparaflin with the absorption mixtureof propylene and concentrated sulfuric acid in the presence of concentrated sulfuric acid under alkylation con-' ditions of operation to efiect alkylation ofthe isoparaflin with said propylene, said-alkylation 7 reaction being carried out at a temperature between about 50 and about 60 C. and in the presence of sulfuric acid of such concentration that the percent concentration of the acid used plus one-seventh of the temperature used in degrees centigrade equals a numerical value of at least 3. The process 'of synthesizing hydrocarbons of gasoline boiling range which comprises combining propylenewith concentrated sulfuric acid to form diisopropyl sulfate and reacting a light isoparaifin with said diisopropyl sulfate in the presence of concentrated sulfuric acid under alkylation conditions of operation to effect alkylation of said isoparaflin with said propylene, said alkylation reaction being carried out at a temperature between about 50 and about 60 C. and in the presence of sulfuric acid of such concentration that the percent concentration of the acid used plus one-seventh of the temperature used in degrees centigrade equals a numerical value of at least 100.

ALFRED W. FRANCIS. 

